Octane upgrading by isomerization and hydrogenation



United States Patent US. Cl. 208-62 4 Claims ABSTRACT OF THE DISCLOSURE Isomeric mixtures of C and/ or C alkanes and alkenes are isomerized to increase isoalkene content, and are then hydrogenated to change alkenes into alkanes. The process is useful in treating mixtures having at least 10% normal alkenes.

Isomerization suitably is carried out over a catalyst chosen from the oxides, acid-treated oxides, or fluorides of elements from Group III and Group IV of the Periodic Table, and mixtures thereof. Isomerization conditions are within the ranges of 70 to 800 F., to 500 p.s.i.g., and 0.1 to 10 v./v./hr. Pre'ferred conditions are 600 F., 10 p.s.i.g., and 1 v./v./hr., over acidified alumina.

Hydrogenation suitably is carried out over a catalyst chosen from Groups VI and VIII of the Periodic Table, and mixtures thereof. Exemplary of suitable catalysts are cobalt (eg, as cobalt molybdate), nickel, platinum, and palladium. The catalyst may be supported on an inert support such as alumina, kieselguhr, etc. Hydrogenation conditions are within the ranges of 70 F. to 700 F., 0 p.s.i.g. to 1000 p.s.i.g., and 0.1 to 10 v./v./hr. Preferred conditions are 550 F., 400 p.s.i.g., and 1.5 v./v./hr., over a supported cobalt molybdate catalyst.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the improvement in motor octane of gasoline blend stocks, particularly isomeric C alkanes and alkenes in admixture, isomeric C alkanes and alkenes in admixture, and hydrocarbon streams containing isomeric C and C alkanes and alkenes. Isomers of both C and C alkanes and alkenes may be present in the blend stock.

Description of the prior art The hydrogenation of C -C gasoline blend stocks to saturate alkenes is well known in the art. This hydrogenation step reduces the sludge-formation tendency of the resulting fuel, and increases the motor octane number as well. However, I am not aware of any suggestion prior to my invention that the motor octane number of a C to C gasoline blend stock could be improved by isomerizing a substantial portion of the normal alkenes into isoalkanes before hydrogenation.

Myers, in US. Pat. 3,242,066, suggests the use of molecular sieves to remove straight-chain constituents from reformed naphtha. This procedure is characterized by a loss in volume of resulting blend stock and is not as desirable as the procedure of the present invention.

BRIEF DESCRIPTION OF THE DRAWING The single drawing is a schematic representation of the process of the present invention, shown as a flowsheet.

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SUMMARY OF THE INVENTION The present invention is directed to the upgrading of C and C gasoline blend stocks. Using a C blend stock as an example, the blend stock will contain normal pentane, isopentane, normal pentene, and isopentylenes. Since light alkenes produced for gasolines are usually obtained from catalytic cracking operations at temperatures approaching 1000 F., the concentration of the various olefin isomers will tend to reflect thermodynamic equilibrium at those temperatures. A typical pentylenes stream from a catalytic cracking unit will have the composition shown below:

The ASTM D-357 motor octane of the mixture shown in Table I (with 3 cc. of tetraethyl lead) is 87.1. Hydrogenation of the mixture saturates the alkenes, giving a saturated mixture having a motor octane of 95.2. By the practice of the present invention, however, a motor octane of 97.8 can be obtained.

In order for the present invention to provide a substantial improvement in motor octane, the base stock must contain at least 10% (by volume) of a normal alkene. It is also preferred that the iC /nC ratio be less than that indicated by thermodynamic equilibrium. The higher the proportion of normal alkenes in the base stock, the more beneficial will be the present inventiomBy contrast, the prior art method of hydrogenation alone is least effective when the normal alkene content is maximized. Thus, the present invention provides a process for markedly improving blend stocks which hitherto have been improved slightly, if at all, in motor octane number.

The eflectiveness of the present invention can be appreciated by advertance to Table II, which compares the motor octane number of normal alkanes and alkenes with the corresponding isoalkanes and alkenes.

AS'lM Motor Octane, 3 cc. TEL (tetraethyl lead).

Note the substantial loss in motor octane which results from hydrogenation of nC and the substantial increase in motor octane which results from isomerization before hydrogenation. The prior art process of hydrogenation converts normal alkenes into the corresponding normal alkanes without isomerization of the normal alkenes into the branched chain isoalkenes. By the present process, however, about 50% of the normal alkenes would be isomerized into the desirable isoalkenes before hydrogenation. For example, isomerization of the C mixture of Table I to thermodynamic equilibrium at 600 F. produces a product of the following distribution:

TABLE III.-ISOMERIZATION PRODUCTS 2 After hydrogenation.

The increase in motor octane after hydrogenation is due to the increased proportion of isopentylenes (which, upon hydrogenation, yield isopentane).

Isomerization The isomerization step is carried out over a catalyst which allows the use of temperatures at which thermodynamic equilibrium favors the production of isopentylenes. Suitable catalysts are the oxides, acid-treated oxides, or fluorides of elements from Group III or Group IV of the Periodic Table. Prills of about inch to 4 inch diameter are preferred. The catalyst may be supported on an inert support such as alumina, kieselguhr, etc.

Isomerization conditions are chosen to favor the production of isoalkenes. Generally, lower temperatures favor such production, but the time needed to reach thermodynamic equilibrium also increases as the temperature is lowered, so a balance must be struck between these factors. Generally, the isomerization will be carried out at temperatures within the range from 70 F. to 800 F., at pressures within the range from O p.s.i.g. (atmospheric) to 500 p.s.i.g., and at space velocities from 0.1 to v./v./hr. (volumes of hydrocarbon per hour per volume of catalyst). The reaction is usually carried out in the vapor phase. Preferred conditions are 600 F., 10 p.s.i.g. and 1 v./v./hr.

A preferred catalyst is acidified alumina. The catalyst is produced by treating alumina having a low sodium 0.l%) content (in prills or pellets) with 5% HF and then activating or calcining at 500 C.

Hydrogenation The hydrogenation step may be carried out in many ways well know to the art. Suitable catalysts are chosen from Groups VI and VIII of the Periodic Table, such as nickel, cobalt molybdate, platinum, palladium and nickeltungsten. Catalysts may be supported on inert supports such as alumina, kieselguhr, etc. Hydrogenation conditions include a temperature within the range from 70 to 700 F., a pressure within the range from 0 p.s.i.g. to 1000 p.s.i.g., a space velocity from 0.1 to 10 v./v./hr., and a hydrogen treat rate from 500 to 5000 s.c.f./b. Preferable conditions, using supported cobalt molybdate as a catalyst, are 550 F., 400 p.s.i.g., 1.5 v./v./hr., and 1500 s.c.f. of hydrogen per barrel of hydrocarbon feed. Hydrogenation is carried out in the vapor phase.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawing, an admixture of C hydrocarbons such as those shown in Table I is introduced by way of line 102 into an isomerization zone 104. Within the isomerization zone is contained a bed 106 of isomerization catalyst, preferably acidified alumina. The admixture of C hydrocarbons is passed over the bed of catalyst under isomerization conditions, such as a temperature of 600 F., a pressure of 10 p.s.i.g., at a space velocity of 1 v./v./hr., whereby a product is obtained which is enriched in isopentylenes, as is shown hereinabove in Table HI. The products of isomerization are passed from the isomerization zone 104 by way of line 108, admixed with makeup hydrogen, which is introduced by way of line 110, and introduced into hydrogenation zone 112.

Within the hydrogenation zone is contained a fixed bed of a hydrogenation catalyst, such as cobalt molybdate supported on alumina (e.g., Nalco 471). In the hy drogenation zone, hydrogenation conditions such as a temperature of 550 F., a pressure of 400 p.s.i.g., a space velocity of 1.5 v./v./hr. (hydrocarbon basis), and a hydrogen treat rate of 1500 s.c.f./b. of hydrocarbons are emplyoyed. The effluent from the hydrogenation zone is passed by way of line 114 into a condenser 116, from which an admixture of liquefied hydrocarbons and gase ous hydrogen are passed by way of line 118 into a separator 120.

From the separator 120 the hydrogen stream is removed overhead by way of line 122, recompressed in compressor 124 and recycled into the hydrogenation zone by way of line as aforesaid. Makeup hydrogen is added by way of line 126, while a bleed stream of deline 128.

A blend stock of improved motor octane number is removed from the bottom of the separator by way of line 130.

The efiicacy of the present process may be seen by advertence to the examples given below.

EXAMPLES Example 1-Isomerization An admixture of C hydrocarbons having the analysis shown in Table III as feed is subjected to isomerization over an acidified alumina catalyst under the following conditions: a temperature of 600 F., a pressure of 10 p.s.i.g., and a space velocity of 1 v./v./hr. The catalyst is employed in the form of pellets having a diameter of about inch. After equilibrium conditions have been reached, a sample is taken and found to have a product distribution substantially as shown in Table III under Product.

It is thus seen that the isomerization increases the isopentylene content from 42% to 54%, while the normal pentylene content is reduced from 24 /z% to 12 /z%.

Example 2-Hydrogenation The admixture of C hydrocarbons shown in Table I was hydrogenated in the vapor phase over a catalyst consisting of supported cobalt molybdate, under conditions of hydrogenation including a temperature of 550 F., a pressure of 400 p.s.i.g., a space velocity of 1.5 v./v./hr., and a hydrogen treat rate of 1500 s.c.f./b. The hydrogenation was carried out in a stainless steel tube having an inside diameter of 1 inch, and the catalyst was in the form of pellets having a diameter of /s inch. After equilibrium had been reached, the product was sampled and found to have the following composition:

Vol. percent Example 3 The isomerized product of Example 1 is hydrogenated under the same conditions as those employed in Example 2, and a product is obtained having the following composition:

Vol. percent Note the increase in the ratio of isopentane to normal pentane from 2.4 (Example 2) to 4.7 (Example 3).

From the examples above it is seen that the net increase in motor octane number is 10.7 (from feed 89.7 to product 97.8) by the present process, as compared to 8.1 by hydrogenation alone.

Having disclosed my invention, including a preferred embodiment thereof, what is to be covered by Letters Patent should be determined not from the specific examples herein given but rather by the appended claims.

I claim:

1. A process for improving the motor octane rating of a gasoline blend stock consisting essentially of C and C straight and branched chain hydrocarbons, wherein at least 10% of said hydrocarbons are unsaturated straight chain hydrocarbons, which comprises:

in an isomerization zone, isomerizing a substantial portion of said unsaturated straight chain hydrocarbons into the corresponding branched chain unsaturated hydrocarbons by contacting said blend stock with an isomerization catalyst chosen from the group consisting of the oxides, acid treated oxides and fluorides of elements of Group III and Group IV of the Periodic Table, and mixtures thereof,

under isomerization conditions including a temperature of 70 to 800 F.,

a pressure from 0 to 500 p.s.i.g., and

a space velocity from 0.1 to 10 v./v./hr.,

and thereafter in a hydrogenation zone hydrogenating said blend stock in contact with a cobalt molybdate catalyst under hydrogenation conditions including a temperature of 550 F., a pressure of 400 p.s.i.g., a space velocity of 1.5 v./v./hr., and a hydrogen treat rate of 1500 s.c.f./b.

2. A process in accordance with claim 1 wherein the isomerization catalyst is acidified alumina.

3. A process for improving the motor octane rating of a gasoline blend stock consisting essentially of C and C straight and branched chain hydrocarbons, wherein at least 10% of said hydrocarbons are unsaturated straight chain hydrocarbons, which comprises:

in an isomerization zone, isomerizing a substantial portion of said unsaturated straight chain hydrocarbons into the corresponding branched chain unsaturated hydrocarbons by contacting said blend stock with an isomerization catalyst chosen from the group consisting of the oxides, acid treated oxides and fluorides of elements of Group III and Group IV of the Periodic Table, and mixtures thereof, under isomerization conditions including a temperature of to 800 F., a pressure from 0 to 500 p.s.i.g., and a space velocity from 0.1 to 10 v./v./hr., and thereafter in a hydrogenation zone hydrogenating said blend stock in contact with a hydrogenation catalyst chosen from the group consisting of cobalt molybdate, nickel, platinum and palladium,

under hydrogenation conditions including a temperature from 70 to 700 F.,

a pressure from 0 p.s.i.g. to 1000 p.s.i.g.,

a space velocity from 0.1 to 10 v./v./hr., and

a hydrogen treat rate from 500 to 5000 s.c.f./b.

4. A process in accordance with claim 3 wherein the isomerization catalyst is acidified alumina and the hydrogenation catalyst is cobalt molybdate.

References Cited UNITED STATES PATENTS 3,420,769 1/ 1969 Manne 208-144 2,865,837 12/1958 Holcomb et al. 208-141 2,909,583 10/1959 Bleich 260-68374 3,180,819 4/1965 Slaymaker et al. 260683.74 3,248,316 4/1966 Barger et al. 208-143 FOREIGN PATENTS 248,938 12/ 1960 Australia.

r HERBERT LEVINE, Primary Examiner U.S. Cl. X.R. 

